Reflective imaging devices, also known as special light modulators, produce a viewable image by locally altering the reflection of light. One useful device of this type is the liquid crystal display, or LCD, in which light entering the display is either transmitted, reflected or blocked, in an imagewise manner, by electronically addressed pixels of liquid crystalline material sandwiched between polarizers, thereby forming a visible image on the display.
LCDs are often illuminated by light which enters one major surface, called the back side, of the LCD, and leaves the other, or front side, where the viewer resides. It is also possible, by means of suitable reflectors, to illuminate LCDs from the front, or viewing, side, and produce an illuminated image by means of ambient light reflected by the reflector, which is commonly called a back reflector. LCDs illuminated in this way are commonly called reflective LCDs, or RLCDs.
Both specular and diffuse back reflectors have been used, and each suffers certain disadvantages. Specular back reflectors may produce a metallic image appearance, may reflect images of objects located behind or above the viewer, and may provide unacceptably limited viewing angles, which may vary with specific ambient lighting conditions. Moreover, specular reflectors reflect incident light in such a way that the viewer's head may block incident illumination needed for best viewing. Diffuse reflectors, on the other hand, have the disadvantage of inefficient light utilization, in that they may diffuse light into locations in which viewers are unlikely to reside, thereby depriving more desirable viewing positions of illumination. These disadvantages are reduced in U.S. Pat. No. 4,298,249, which provides a back reflector having tilted reflecting surface strips, along with diffusing surface structures, so as to reflect incident light at angles which enable the display to be viewed from a more suitable position. Similarly, U.S. Pat. No. 6,204,903 discloses reflective and partially reflective surfaces having various structural shapes that direct reflected light in particular directions. In order to accommodate a variety of lighting conditions, U.S. Pat. No. 5,128,787 discloses a reflector having structures of various angles, so as to reflect light from a variety of sources into the desired viewing positions. The disclosed structures also have the advantage of reducing the effects of glare, since they enable the image to be viewed from positions outside of the areas receiving unwanted specularly reflected light from the various surfaces and interfaces of the display.